In February 1994, Baxter Healthcare Corporation, withdrew all of their Immune Globulin Intravenous (Human) (IGIV) lots which include Gammaguard (manufactured from commercial plasma, both Source Plasma and recovered plasma) and Polygam (recovered plasma from American Red cross) because of the reports of possible hepatitis C virus (HCV) transmission. Since then, we have been working intensively with Baxter's IGIV and sera from some recipients, and tried to understand the rationale for such outbreak. Previously we did not detect HCV RNA in any of the 3 lots of Gammaguard and 2 lots of Polygam made during 1988-89. Thus far, we have assayed a total of 40 lots of Gammaguard by PCR. Reconstituted samples from 31 lots were also given to Hepatitis Laboratory (HL) for PCR and for assaying anti-HCV reactivity by RIBA-2. Gammaguard lots manufactured since 1992 were found to be anti-HCV negative. For lots manufactured in 1993, we detected HCV RNA in 15 of 26 lots; among them, 21 lots were assayed by both labs, and we detected 12 positive while HL detected 13 positive (PCR results from 14 lots were agreeable between 2 labs). For lots made during 1988-1992, we found HCV RNA only in 1 of 14 lots; among 10 lots assayed by both labs, we found 1 positive while HL found the same lot and additonal 2 lots positive. All of our 15 positive lots and 12 of HL's 13 positive lots were manufactured since April 1993, which coincides with the time when Baxter manufactured IGIV lots 100% derived from multiantigen anti-HCV screened plasma. HCV RNA was also detected in 16 of 18 recipients'sera. Therefore, we strongly suspect that protective antibodies for HCV might have been removed from IGIV because of multiantigen screening of plasma. We found 1 of 4 gammaguard lots prepared from recovered plasma was positive for HCV RNA while HL found 3 lots positive. However, by limiting dilution we identified 8 lots prepared from Source Plasma having higher levels of HCV RNA. We are in the process of characterizing the HCV RNA present in 2 implicated lots which we determined to have the highest levels of HCV RNA among all.